Tuesday, March 28, 2017

SP 2424 (Part 2) - Roof A/C Hatch Installation

The next step in upgrading the SP 2424 is installing a roof hatch for the A/C system.  Many SP cars were upgraded in the early 1950s and by the mid to late 1950s the design of the roof hatch had changed to a "high" style one with a combing or flange around the opening into the A/C equipment to keep water and snow out.  The later style was also easier to use with a set of butterfly doors that hinged away from the car's centerline.

Here's the link for those of you that missed SP 2424 (Part 1) - Truck Conversion.

OwlMtModels #4001 SP Roof A/C Hatch (Brass) added to SP TTG artic chair car - Boyd Reyes Photo

The Parts - 3D Printed to Order!

The company I work for was asked by a customer to produce these hatches for some of his models.  They are now available in 3d printed lost-wax brass single casting (OMM #4001) $21.88 or a pair of hatches in High-Def Acrylate (HDA) plastic (OMM #4002) $12.95 from the Owl Mountain Models storefront at Shapeways.  The OwlMtModels website is also updated with a new 3D Printed Detail Parts page.

OwlMtModels' 4002 SP Roof A/C Hatches 3d printed in HDA plastic for $11.95 for a pair of hatches.

One point should be made here is that each set of parts is printed or cast as a one-off part, not mass produced, so this is reflected in the higher cost per unit for these "Printed-on-demand" parts.

The backs of the hatches have the remains of the support structure for printing, this will be easily sanded away.

I ordered a pair of the OMM #4002 plastic parts which arrived in about 12 days from the printer in New York.  The HDA material was still slightly soft, so I planned to clean them up and then let them UV cure in the sun for another 30-60 minutes with rubber bands holding it to the car roof.  This would hold the thin parts in the correct shape for the SP 2424's roof once the material fully cured.

If I just left the part to fully cure in the sun without being rubber banded to the car, I'm worried that the part will cure in a warped or twisted condition.  Once cured, in my experience, trying to fight the "set" that a part's taken is a real problem.  In a way I'm glad the parts came slightly too soft, so I can be sure to have them cure in correct alignment with the car's roof.

In this photo the bowing of the parts can be seen.  This will be corrected during pre-installation.

The next step with the soft hatches is to file smooth the bottom of the hatch so it will fit snuggly down onto the SP 2424's roof.

Back side of Hatches with support material to be removed

The bottom of the hatches needs to be cleaned up somewhat.  I did it with a small file.  The material was still soft enough that the parts flexed nearly flat.  Supporting the top of the part while doing this is a good idea.  Also make sure not to take too much off and change the contour of the part.

Here's the partly filed down underside.

I also filed away the sprue that was connecting the two parts from the side of the part.  I apparently slightly beveled the last 1/8" or so on one side of these hatches during this cleanup process.  The master file at Shapeways has been updated to fix this possible issue.

Here's the smoothed Hatch bottom.

Modifying the SP 2424's Roof

The new hatch will need to sit flush with the roof of the SP 2424.  There are two roof ribs in the way of doing this.  I also need to mark the centerlines of where the hatch will go.

Using my mechanical pencil I mark where the centerline of the roof is.  This will match up with the centerline joint in the roof hatch.  I held the hatch in place and marked around the hatch with my pencil.  This will create a mark about 0.015" away from the hatch edge.

Here's the roof marked with pencil and Sharpie.  The hatch is laying off to the side also.

I used a Sharpie to make the markings inside the lines darker for the camera to see.  The next step is to carefully cut the ribs down.  They need to be removed almost all the way out to the lines.  I marked the edges with an Xacto #11 blade, scoring across the ribs, then used a file on the portions within the lines to quickly get down even with the roof.
Here's the roof after filing is complete.

If the ribs are slightly too short, it shouldn't be noticeable when the hatch is in place with the slight overhang on all sides.

Sun Post-Curing

The next step was to let the parts UV cure a bit more in the sun.  I used a rubber band around the car body and a piece of styrene strip to rest the truck frame level against, so as not to damage the truck bolster assembly built in SP 2424 (Part 1).

After about 30 minutes in the morning sun, I moved the rubber bands over to allow the previously covered areas of the hatch to cure some more.

I considered the parts done when I couldn't scratch the surface of the hatch with my finger nail anymore.  The part is still somewhat "spongy" but I believe this is from the part only being 0.030" or so thick.  I still treat the part somewhat carefully as I don't want to "crush" the arch in the part which will match the roof contour.

Sanding Prep

Generally 3d printing does require some cleanup on the parts, rather the same way that injection molded parts sometimes have flashing and injection gate marks.  I started by cutting the two hatches apart with sprue cutters.  The "stepping" from the printing can be seen in the top surfaces of the hatches.  This looks rather like wood grain.  Not much can be done on the top of such a large radius arc to prevent this from happening.  It is nice to see that the brass OMM 4001 parts had very minimal stepping.

The brass OMM 4001 parts have minimal stepping which painting easily covers.

With the HDA plastic parts now cured more, I felt better about doing some sanding.  I primed one of the two hatches with UP Harbor Mist Gray to see how bad the stepping was.  The second hatch I started with sanding down before priming.

There was some stepping so I did some light sanding.

It looks worse than it is, but I decided to do some light sanding anyway.

Primed hatch sanded around the handle details.

The sanding was done with a 600-grit foam sanding stick.  This only took a couple of minutes.  I was careful to brace the part well as it was still very flexible even after curring more in the sun.

Painting the Hatches

I painted the bottoms edges of the hatches first from below.  Then painted the tops of the hatches.

Here are both hatches after painting.  The left one looks like I need to rescribe the center panel line again.

I installed one of the hatches on the SP 2424 with ACC.  The HDA material likes ACC as it quickly bonded the hatch to the roof.  The slightly rough bottom of the filed hatch and filed mating area on the car roof probably helped this.

Here's the hatch installed.

Touching Up the Roof Paint

The next step was to touch up the roof of the car.  I'd left the pencil marks extended out past the end of the hatch so it was easier to line up.  Also I had some light weathering on the car roof which I wanted to paint over for a fresher shopped look for the whole car.

Here's the Hatch installed and waiting to touch up the roof to cover the pencil marks.

Masking was done with blue tape.  I didn't worry too much about covering and sealing down the edges, as I planned to shoot the Harbor Mist Gray from a low angle.

SP 2424 masked and ready to touch up the gray roof.

I carefully removed the masking from the car sides.  One of the hand grabs next to the door decided to choose that moment to pop out of the holes and the short nib ends were too short to easily slip back in.  I just replaced it with a section of 0.014" steel wire.  Reviewing these pictures also reminds me there's a ladder rest grab missing on the roof.  I'll have to replace that at some point.

All Shopped and Ready to Go!

Detail view of the finished and painted Hatch.

Remember what the car looked like before the upgrades?  Here it is with the original Athearn-Genesis "Triple-Bolster" trucks.

Here are the current side views of SP 2424 with the new Walthers GSC trucks and OMM roof hatch installed.  It certainly looks a bit different now with the new trucks and extra hatch on the roof.

Left side SP 2424

Right side SP 2424

I should mention in closing roughly how long it took for me to do each of the steps;
Part sanding and prep (2 hatches) = ~10 minutes
Modifying the roof of the car (marking & removing ribs) = ~10 minutes
Rubber banding parts to roof and UV Curing = two blocks of 30-45 minutes (unattended) - Note this was doubled for curing the second hatch because I only modified one car roof.
Pre-Painting Hatches off car (2 hatches) = 10 minutes (or less) with air brush
Mounting Hatch to car (1) = ~3 minutes
Masking and airbrushing whole roof to blend new and old colors = ~15 minutes

Total time spend = ~ 1.25 hours working time, plus UV curing time.  It is certainly easily done in an enjoyable few short afternoons with drying times in between.

This wraps up Part 2 of my SP 2424 blog post.  In the next part SP 2424 (Part 3) - Radio Antenna Stanchions I cover more on detailing the roof.

Jason Hill

Related Links:

SP 2424 (Part 1) - Truck Conversion

OwlMtModels Shapeways Storefront

Index Page for SP Lightweight Passenger Car Models - HO

SP 2436 (Part 1) Upgrading Athearn-Genesis 77-C-3 Chair Cars

Wednesday, March 22, 2017

SP 2424 (Part 1) - Truck Conversion

This is a post about one of those models we've all had for years and it's a very nice model.  Then over the years more research has come out about the prototype and the issues start to bug you more and more, until you finally do something about it.  Well, that's pretty much the story of my model of SP 2424.

Where The Car Started

It started as one of the three road numbers offered for the yellow and gray SP "City" scheme in Athearn-Genesis's first run of 77-C-3 chair cars.  Several prototype cars of this class were painted into this scheme over the years.  Not knowing much about which number to choose at the time I picked up a SP 2424.  I probably should have chosen another number which was painted into the scheme earlier, but I didn't.

Roughly Out-Of-Box Athearn-Genesis 77-C-3 model of SP 2424.  I added some window shades and light weathering.

The model comes with the "triple-bolster" style trucks typical of the 1937-1941 Pullman built Daylight cars.  The SP 2424 was first painted into the COSF (City of San Fransisco/Overland) scheme in June 1955 and was one of the cars heavily reconditioned for the assignment.  Earlier 77-C-3s assigned to City service were not upgraded as the 1955 group were.

The Historical Upgrades

The upgrades consisted of changing the seating from the (normal) 48-seat Chair Car configuration to the 40-seat deluxe "Leg Rest" configuration for cross country travel between San Fransisco and Chicago.  Mechancially the car was also refitted with new GSC 41-NDO trucks with Budd disc brakes for higher speed running.  These trucks were also more common on the newer City consists, so the UP and CNW carmen could inspect and repair the cars easily while on the eastern end of the run in Chicago.

Here's the model laid over the SPHTS Vol.1 photo and the new Walthers trucks laid under the Athearn trucks.

The Model Upgrades

Weathering The Diaphragms

I decided to take a few minutes and weather the striker plates of the diaphragms with a few different techniques.

Striker Weathering

The end of the car doesn't usually get cleaned very well by the car washers between trips, so I weathered it a bit heavily.  The strikers are usually bare steel, which will be any variety of rusty on cars that don't get used much, to fairly shiny and polished on cars that are in regular service and are always rubbing on the striker of the next car in the train.

The strikers were also greased, so often I will use black and dark gray colors to simulate the slobbers of grease that coat the strikers of well maintained cars. - think of the look of a 18-wheeler's 5th wheel hitch - that level of grease!

Prismacolor Pencils, this set was about $15.  Additional color pencils can be had for $1-2 in a multitude of colors!

I used silver Sharpie for the basic bare metal striker, with black Sharpie and Prisma pencil for the rubber gasket which keeps water and such from dripping on the passengers.  Additional sienna brown and dark brown color pencils are used to get the shades of rust on various parts of the striker which aren't being rubbed clean.

Walthers GSC 41-NDO Trucks

The Athearn-Genesis underframe and trucks use pins and very small springs to conduct power from the track up to the lighting system in the car.  The replacement Walthers GSC trucks (920-2200 blk & 920-2201 silver) don't lend themselves to this style of power transfer easily.  Instead I'll be using my standard methods of power pickup which I will cover in a later post.

The trucks were painted a dark gray-black and then airbrushed with Harbor Mist Gray at angles to keep the shadows.

The trucks were painted a gray-black and then sprayed from above and below with Harbor Mist Gray (standard underframe color for COSF cars).  This way the black colors stayed in the spring and other deep recessed details of the trucks.  I also painted the wheel faces, as the truck are roller bearing, which do not leak oil the same way that plain bearings do.  A light wash of black over the springs and the bearings brings out the depth.  This was needed since the coat of gray did a little too well covering some of those areas.

Painted and modified bolster on the Walthers 920-2200 GSC 41-NDO trucks.

This pair of trucks' wheel treads cleaned with thinner and a bit of paper towel.  This is a good habit to get into because most metal wheels are not cleaned after being manufactured these days.  There's often a coating of machine oil on them which also doesn't do any good for the cleanliness of a model railroad.  Letting the wheels run themselves clean on a layout is a good way to make everyone's engines dirty and operate poorly!  Not to mention make the other operators mad at you!

Also be sure the wheels roll freely in the sideframes.  Lubricating the trucks with a small drop of light oil on the bearings helps reduce friction and also improve conductivity for the lighting system.  Also remember to check the gauge of the wheelsets.

New Bolster Arrangement

The main change with converting the model to the new trucks is changing the bolster arrangement on the Walthers trucks.  I start by measuring and cutting a pair of small pieces of 0.020" styrene sheet to fit on the bearing surface of the Walthers truck bolster.  I drill a clearance hole for a 2-56 screw through the center of this plate, this will reduce the oversized hole that comes with the Walthers trucks down to my preferred mounting screw size of 2-56.

The car already has body mounted couplers adjusted to the correct length for close mating of the diaphragms, as seen in the photo below.

In this photo the new spacing bolster block is to the right of the body bolster pad.

I had already made some modifications to the Athearn-Genesis body bolsters to lower the car slightly before I started on this truck conversion project.  After modifying the truck bolster, I estimated that the body bolster was about 0.080" too short.  I cut a pair of blocks from 0.080" sheet styrene to about 0.125" square.  This doesn't need to be too accurate, as it need to clear the inside stepped edges of the top of the styrene truck bolster pad I added to the trucks.  The blocks are drilled with a clearance hole for 2-56 thread as well.

The body bolster block is placed on the bolster and a 2-56 screw is ready to go in the truck bolster.

While I glue the bolster block to the body on most of the cars that I use this style of conversion, on this car I have decided not to at this time.  I chose to do this partly because I already had lubricated the body bolster with graphite and I doubt that gluing will be very effective.  Also with it lubricated already, the truck should be more free than if I tried to glue it and force all the movement to be made at the lower bearing.  This is also why I chose to drill the spacer block with a clearance hole instead of a tapped hole, which I would do if I was going to glue it to the underframe as part of the body bolster.


Here's the car reassembled with the new trucks and car adjusted to ride at the right height.  Currently the lighting systems in the car are disabled because I've not reconnected the trucks to the interior lighting system.  That will be completed later.

Left side of SP 2424 with new trucks.

Right Side of SP 2424 with new trucks

That will do it for this post about the SP 2424 (Part 1).  In SP 2424 (Part 2) I cover installation of an OwlMtModels Roof A/C Hatch.  In other future posts about this car I will work on rebuilding the underbody details, as well as rearranging the seating inside for the correct 40-seat configuration.  While this car is historically a few years too new for my main era of modeling (1948-1953) because of the paint scheme, I might as well upgrade the details to make it correct for its era.

Jason Hill

Related Links:

Mt.Nebo (Part 1) 10-Section-Obs-Lounge - Shows how to tune Walthers Trucks

Tuesday, March 14, 2017

SP 4239, a Mk-3 IMRC AC-10 (Part 1) - Damage Control

In early February 2017, I was able to sit down with a friend and help him with his AC-10 that had a damaged main driver.  Together we worked on repairing it and I took some photos along the way.  A month or so ago, I published my page about the IMRC Cabforwards - 10 Years of Experience.  This is a follow up post to that page.

SP 4239 between runs - Eddie Sims Collection - used with permission.

Mk-3 IMRC AC-10, SP 4239

Driver Damage

Failure of the main crankpin in the driver casting.

The damage took the form of a crack that compromised the grip on the main crankpin of the radial engine.  The entire siderod and main rod assembly including the pin simply fell off the engine.  I happened to have a spare driver and was able to trade it out, replacing the damaged one.

Rebending the Yoke

The yoke is visible between the exhaust steam pipe and the bundle of wires with a 5-10 degree bend in it.

The engine also had a bent radial engine yoke, which is a brass casting.  I was able to bend this back to shape, but something insane had to happen to the engine for this amount of damage to happen to both the driver and equilateral crushing of the yoke from both the right and left sides of the engine.

This was a pain to fix because I had to drop the radial engine from the boiler.  To get to the screw I had to remove the top of the boiler, and the electronic PC board in the smoke box to get to the screw on the sprung stud at the right of the above photo.

Other Damage

To get the drivers out the cover plate had to be removed.  The screws were in so tight that a large amount of force was required to get them out.  I wonder if they're lock-tighted in place or something.  The radial drawbar connection at the main cylinders wasn't able to handle the force required, so it cracked and failed.  I start to wonder at this point if this is part of the damage to the yoke and main crankpin.

Other Modifications

Other modifications to the engine also included rearranging the details in the cab and installing a crew in the engine.  The sliding windows were glued in place to simulate the windows being open and the window sections that held the sliding window parts were removed.

The crew from the 4279 (which is now a scenic display model) were transferred to the 3rd run engine.  Unfortunately the damaged drawbar connection between the radial engine and the main cylinder block was changed between the 1st run and 3rd run engines, so a trading of parts couldn't be made.  So that repair will have to wait until replacement parts can be acquired by the engine's owner.

The old IMRC Mk-1 AC, SP 4279 minus her tender sits in the Bakersfield Roundhouse undergoing repairs.

SP 4279 many years ago became a "parts engine" to use when other parts on IMRC engines failed, broke, or dropped off.  Note the missing front left side rod pin screw and eccentric rod screw have been removed.

Conclusion - Mk-3 IMRC AC-10, SP 4239

The SP 4239 shoving hard at the rear of an SP freight on the Modoc line.  Eddie Sims Collection used with permission.

Hopefully the IMRC SP 4239 will soon enter service and then we can see how the IMRC's Mk-3s perform.

Jason Hill

Related Pages and Links:
IMRC Cabforwards - 10 Years of Experience

Wednesday, March 8, 2017

Correcting Sunset Models SP Mk-2 & Mk-4

Recently there was a post on-line asking more about how correct the Sunset Models SP Mk-2 is.

In my previous post about Modeling SP Road Switchers (Part 2) - Medium Steam, I briefly touched on the issues with these models.

SP 3302 Mk-2, with slanted cylinders.  About 1946 photo, silver smoke box, with "Lines" on tender - Eddie Sims Collection

Ex-Arizona Eastern 903, renumbered as Second SP 3239 in 1924.  Post-June 1946 photo - Eddie Sims Collection

According to Brown Book of HO scale brass locomotives in 1983 Sunset Models imported 290 Mk-2 and and in 1984 an equal numbers Mk-4.  There seems to have been a mix-up at the factory in which the valve gear and cylinders were swapped between the two runs of Mk-2/4.  The two models that I received from a customer to work on had the outside valve gear on the boiler and frame of the Mk-2 and the inside cylinder (correct for some Mk-2s, but not Mk-4s) on the model with the boiler and frame details consistent for the Mk-4.

Sunset SP Mk-2 Model "Long"

Box Label from Sunset Model;s SP Mk-2 2-8-2

Left side of Sunset Mk-2, corrected for SP 3207.

From what I can gather the Mk-2s were the only class fitted with the inside valve cylinders, following the Stephenson design, but with very weird "crossover" valve gear to outside eccentric motion at the main driver.  The way the two models I show here were sent to me, the Mk-4 (AE version) had the inside valve cylinders which is NOT correct for any photos I've seen at all.  I will quickly add here that some of the Mk-2s with inside valves cylinders were rebuilt with outside valved cylinders like the Mk-4s always had.  All of the Mk-2s and Pacific Lines (SP built) Mk-4s seem to have the large sand domes.

Right side of Sunset Mk-2, corrected for SP 3207.

Notice that the Mk-2 framed engines with the large sand dome and "sport cabs" are about 12" scale inches longer than the (AE) Mk-4 model below.  The prototype photos below seem to bear this out, that there were two different length engines, the "longer" of which were the engines built for originally for the SP as Mk-2 and Mk-4.  I'll discuss the "Short" engines below.

Sunset SP Mk-4 Model "Short"

Box cover for Sunset Mk-4 2-8-2

SP 3224, Mk-4 with right side air pump. - Eddie Sims Collection

Notice that the SP 3224 above has the large sand dome, airpumps on both sides, and a "sport cab".  The engines built for the SP as Mk-2 and -4 seem to have longer lines as well compared to the model below.

Sunset Models SP Mk-4 after valve gear swap - corrected for SP 3237 (2nd), ex-AE 901.

Sunset Models SP Mk-4 after valve gear swap - corrected for SP 3237 (2nd), ex-AE 901.

Given that the "Short" framed model's details line up better to the ex-AE 901-905 engines (SP 3236-3240), I would say that the Sunset Models engine with the small sand dome, two air pumps on the left side, and square cab is really a model of the Arizona Eastern built engines.

Swapping Valve Gear & Cylinders 

To fix the issue of the "Mk-4" having the wrong domes and wrong inside valve cylinders, I decided to swap the frames of the two engines.  This revealed another issue.  The "Mk-4" with the small sand domes is about 12" scale inches shorter than the other engine!  Swapping the frames is out.  I then decided to look again at my books and photos, coming to the conclusion that with the parts I could swap the valve gear between the two models was actually fairly simple.  Here's the basic steps to do this swap:

Remove in Inner Smokebox screw.
Remove Smokebox-Cylinder Screw which will allow the cylinders and smokebox of the boiler to separate.

Remove Rear Cab Screws

Next, remove the two screws in the rear wall of the lower cab, this will release the boiler and cab from the frame.

The Left Eccentric Screw is VERY small, but shouldn't be too hard to loosen, do not remove it!

After the boiler is set asside, use a very fine screw driver to loosen the eccentric screws.  Do NOT Remove these screws, they only have to be loose enough to slide off the main crank pin.

Do the same with the Right Eccentric Screw.

Make sure to remove and keep any washes that are between the side rods and main rods safe.  You will need to place them back between the same rods again.  Making notes of this is a good idea!

Remove the Yoke Screws.

Almost there, next, remove the two yoke screws, this will release the valve gear.  Last is the main cylinder blocks.

Lastly, remove the "outer" screw from the bottom of the cylinder block.

Lastly remove the main cylinder block screw.  This is the "outer" one, which has a hole through it for the inner screw which we removed first that holds the smoke box and boiler on.

Follow these steps on the other engine, trade parts and reinstall.

Sunset Mk-2 with inside valve cylinders.

Sunset Mk-4 with outside valve cylinders.

It's possible that the previous owner before my customer bought these two Sunset engines did exactly what I undid in trading the valve gear and cylinders to make a Mk-4 with the "SP-style" boiler and "sport cab"... - however I have heard from other people that the cylinders were swapped from some of the engines when new as well.  Hopefully these photos of the prototype engines and book photo references will help you in sorting out which engine you want to model!

Mk-2 Photos & Ref's

Several Mk-2s were rebuilt with the later Mk-4 style outside valved cylinders.  In these photos both engines have "Sport Cabs" with the slanted front wall to clear access for the staybolts on the rear sides of the firebox.

I'm going to put together a short list of Mk-2 class engines that had the outside valve gear cylinder.

SP 3201 - Photo Feb'52 Lone Pine, SP San Joaquin Valley - Tom Dill, pg.102. 120-SC-type tender

SP 3202 - Inside Valved Cylinders, "Sport Cab", FWH, 120-C-1 Tender. - Eddie Sims Collection (Below)
SP 3202, Mk-2 - Inside Valvegear, FWH, "Sport Cab", 120-C-1 Tender, 1946 - Eddie Sims Collection.

SP 3203 - Outside Valve Cylinders, "Sport Cab", 120-SC-tender. - Eddie Sims Collection (Below)
Mk-2 SP 3203 right side, with outside valve cylinder as Sunset Mk-2 was imported.  Owenyo, CA, Eddie Sims Collection

Mk-2 SP 3202 left side,  clamshell stack, and footboard pilot. Owenyo, CA, Feb 10, 1951, Andrew Brandon Collection.

SP 3207 - Photo Livermore, SP San Joaquin Valley - Tom Dill, pg.18. - Narrow Cylinders

SP 3208 - I believe I have a picture of this engine in the Southern Pacific Steam series on Mk-class engines by Jeff Ainsworth. - which I've misplaced just as I'm writing this.  I will correct this reference when I locate the book again! - The corrected Sunset Model with 120-C-1/2 tender is correct for the photo of 3208 in this reference.

Mk-2 SP 3208 with Mk-4 type Cylinder as Sunset Mk-2 was imported.  Eddie Sims Collection

SP 3211, date unknown, but after June 1946.  Eddie Sims Collection.

Mk-4 Photos & Ref's

Note that the SP built Mk-4s have the large sand domes.  The Ex-Arizona Eastern Mk-4's 3236-3240, had small sand domes and

SP 3216 - Photo Aug-1955 Livermore, SP Golden Empire 1954-1958, published by SPHTS, 2011. Pg.31 120-C-7 tender.
SP 3216 - Photo July '53  Livermore, SP' San Joaquin Valley Line- Tom Dill, pg.18.

SP 3216, with 120-SC tender and large forward mounted sand dome.  Engine out of service. - Eddie Sims Collection

SP 3218 - Photo June'54 Tracy, SP' San Joaquin Valley Line - Tom Dill, pg.25. 120-SC-type

SP 3218, Mk-4, with 120-SC-tender, FWH, and large forward mounted sand dome. - Eddie Sims Collection.

SP 3227 - Photo July-1956 W.Oakland, SP Golden Empire, pg.17 120-C-3/6 tender
SP 3227 - Photo Jan-1953 Little Lake, SP's San Joaquin Valley Line - Tom Dill, pg.101. 120-C-3/6 tender

Right side of SP 3227, Mk-4 with 120-SC-tender with raised bunker, large forward sand dome. - Eddie Sims Collection.

Left side of SP 3227, Mk-4 with square cab and no FWH. - Eddie Sims Collection

SP 3235, Mk-4, "Sport Cab", 120-C-2 tender, large forward mounted Sand Dome. - Eddie Sims Collection.

SP 3236 - Photo July-1956 W.Oakland, SP Golden Empire, Pg.18 120-SC-type tender - no headlight

SP 3237 (2nd) Ex-AE  901 - Photo Lone Pine, SP's San Joaquin Valley Line - Tom Dill, pg.101. 120-C-3/6  I believe there is an additional photo of this engine in the Southern Pacific Steam series on Mk-class engines by Jeff Ainsworth. - which I've misplaced just as I'm writing this.  I will correct this reference when I locate the book again! - The corrected Sunset Model with 120-C-1/2 tender is correct for the photo of 3237 in this reference as well as the picture in Tom Dill's SP'San Joaquin Valley Line.

SP 3239, Mk-4, Ex-AE 903, small sand dome, sqr. cab, FWH. Also note how short the engine looks. - Eddie Sims Collection.

In Closing

From these two photos (SP 3239 above, and Sunset Mk-4 below), it is pretty clear that the Sunset Mk-4 model's boiler was designed to replicate the Ex-Arizona Eastern's 901-905, which were renumbered as SP's Second 3237-3240 in 1924.

To Make the SP 3239 from a Sunset Mk-4, the rear left air pump would need to be replaced with a Worthington FWH.

At least now my customer's two models both have a correct prototype to be finished as and be accurate for.  I really like these small-drivered 2-8-2s, they have really grown on me over the last few years seeing them in more pictures working locals in the areas I'm interested in modeling.

I'm sure I'll be doing more blogs on these two models as they are painted and finished.  This post was mostly to put out some information about the differences between the Sunset Models Mk-2 and Mk-4 models and some photos to show what the real engines looked like at various times in their careers. A big THANKS! to Eddie Sims for the use of the photos in his collection.

Edit: Several followers of the blog have responded to this post and shown their "Mk-4" models that came with outside valved cylinders but the small dome, which they replaced with an after-market dome.  I've also seen one model that came as my customer's did with the Mk-2 "long frame" engine with sport cab and large dome, but fitted with the outside valve cylinders.  So it would seem that there is quite some variation in what Sunset brought in with the two runs of Mk-2 and two runs of Mk-4.

Jason Hill

Related Links:
Modeling SP Road Switchers (Part 1) - Small Steam

Modeling SP Road Switchers (Part 2) - Medium Steam

SP Tender Swapping (Part 1) - A Game for Prototype Modelers

New Drawbar Mount for Athearn-Genesis 120-C-6 Tender

Enjoy the other Night Owl Modeler blog posts as well.